Method of bending sealed glass tubes



1950 H. E. VALENTINE 2,508,127

METHOD OF BENDING SEALED GLASS TUBES Filed June 1, 1949 lrwveh lrorzHarold E. VaLen=tine, Jog fiat A? His A=irirorne5.

Patented May 16, 1950 METHOD OF BENDING SEALED GLASS TUBES Harold E.Valentine, New Malden, England, assignor to General Electric Company, acorporation of New York Application June 1, 1949, Serial No. 96,445 InGreat Britain June 25, 1948 2 Claims.

This invention relates to the manufacture of hermetically sealed lengthsof glass tubing bent to a desired shape and the pressure within which iseither below or is above atmospheric. More particularly, but notexclusively, the invention relates to the manufacture of low pressuretubular electric discharge lamps which are bent to a desired shape.

The bending of the glass tubing in such manufactures has hitherto beenperformed prior to the evacuation or pressure-filling and the sealing ofthe tubes, usually by wrapping an electric heating coil around the partof the tube to be bent, passing current through the coil to heat andsoften the glass, and bending the tube to shape around a former.

But in some cases, especially with long tubes, the manipulation of thebent tube for evacuation or pressure-filling and for sealing is veryinconvenient and the object of this invention is to provide a methodwhereby the bending may be effected after the evacuation orpressurefilling and the sealing despite the low or high pressure withinthe tube.

According to the invention, in order to effect the bending after theevacuation or pressurefilling and the sealing, the already sealed,evacuated or pressure-filled tube is enclosed within a flexible andsubstantially gas-tight jacket at least at the part at which the bendingis to be eflected, the pressure within the jacket is adjusted tosubstantially the pressure within the tube, part of the tube is softenedby heating in any suitable manner and the softened part of the tube andcorresponding part of the jacket are then bent together to give therequired bending for the tube.

The jacket is preferably of cross section not much larger than that ofthe tube so that the bending of the glass tube in the softened state maybe easily effected and controlled. A former may be used in the usualmanner to provide the requisite shape.

The heating means by which the glass is softened is preferably anelectric heating coil lying within the jacket and wound around the partof the tube which it is desired to soften.

For a further understanding of my invention reference may be had to theaccompanying drawing wherein Fig. 1 is an elevation, partly in section,of a tube enclosed in a suitable jacket preparatory to bending the tube,and Fig. 2 is a plan view showing the bending of the assembly of tubeand jacket around a suitable form.

In one method in accordance with the invention, and illustrated in thedrawing, for manufacturing a low pressure tubular electric dischargelamp bent to a desired shape, a straight tubular glass envelope i,already sealed with the electrodes (not shown) and required low pressurefilling therein, is mounted so that part of the tube having an electricheating coil 2 wound around it lies within a flexible bellows typetubular metal jacket 3 of the vacuum-tight kind already known for use inconnection with pumping systems and whose cross section is not muchlarger than that of the tube l. The ends or" this jacket 3 are vacuumtightly closed by rubber bungs l, 4 which fit closely in brass sleeves5, 5 soldered or brazed to the ends of the jacket 3, and the leads tothe heating coil 2 are taken vacuum tightly through insulating tubes orbeads 6, 5 in the bungs 4. In addition a pump connection l is madethrough one or both of the bungs 4. Preferably the heater wire 2 iscovered with braided asbestos to insulate it from the metal jacket 3;and the said wire may be made in strip form. as disclosed, for example,in Patent 2,135,775 to Walker.

In the process of manufacture the flexible jacket 3 is evacuated to thepressure within the tube by pumping and then the pump connection isclosed, a current is passed through the heating coil 2 and when theassociated part of the tube I is softened sufficiently the outer jacketand the tube are together bent around a former 8 (Fig. 2) to the desiredshape at this part.

Alternatively, if the jacket 3 is not completely vacuum-tight it may becontinuously pumped to maintain the desired low pressure within itduring the softening and bending operation.

It will be appreciated that the invention may be applied to themanufacture of bent fluorescent discharge lamps as well as to thenon-fluorescent type of lamp, and to lamps having hot cathodes as wellas to lamps having cold cathodes.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The process of bending sealed glass tubing the pressure within whichis substantially different from atmospheric pressure which comprisesenclosing the tubing within a substantially gastight and flexible jacketclosely fitting the tubing, adjusting the pressure within the jacket tocorrespond substantially to the pressure within the tubing, heating thetubing to soften it, and then bending the assembly of tubing and jacketto the desired shape.

2. The process of bending sealed glass tubing the pressure within whichis substantially different from atmospheric pressure which compriseswrapping an electric heating coil around the tubing and enclosing thetubing within a substantially gas-tight and flexible jacket closelyfitting the tubing, adjusting the pressure within the jacket tocorrespond substantially to the pressure within the tubing, heating thetubing to soften it by passing an electric current through said heatingcoil, and then bending the assembly of tubing and jacket to the desiredshape.

HAROLD E. VALENTINE.

No references cited.

